A. Field of the Invention
The present invention relates to a new and improved assembly for applying hot melt glue to book blocks, and specifically, to a new and improved assembly including a flexible wheel fabricated of a material capable of withstanding the high temperature of hot melt glue without deteriorating and of remaining flexible for applying the hot melt adhesive to book blocks.
B. Description of the Background Art
The assembly of a book with endsheets or end leaves attached to a hard or flexible cover requires several distinct operations. The body of the book must first be collated to provide for proper pagination of the text. The integrity of the assembled endsheets or signatures is then accomplished utilizing existing technology such as adhesive binding, "Smyth" sewing, side wire stitching or saddle stitching. The bound book block is then trimmed on three sides to provide the final size.
The book block backbone is then reconfigured to a specific configuration such as a flatback without joints, a flatback with joints, a round configuration only, or a round configuration with joints. To retain the selected shape placed into the backbone of the book, an adhesive, typically animal glue or hot melt in a film is applied, followed by the application of a reinforcing woven material. This is followed by a film of adhesive to which a liner with head bands is applied. The book is completed by joining the book block with a cover.
The current technology for metering and applying adhesive to the backbone of a book block can be accomplished by several different methodologies. One methodology involves facing the backbone of the book block downwardly while held in a clamp or a belt. In this position, the book block passes over a rigid wheel with a diameter cut to match the contour of the backbone of the book block. The wheel rotates in a bath of adhesive such as animal glue or hot melt and a scraper blade meters the adhesive on the wheel prior to frictional application of the adhesive from the rotating wheel onto the book block. The continuous rotating motion of the glue wheel is typically actuated by cams to cover the backbone from edge to edge without running over the head or tail of the backbone. The wheel size and radius are determined by the bulk of the book block. It can also, however, be affected by the flexibility of the book block. The contour of the backbone of the book block must match the glue wheel to achieve proper glue application since an improper fit can result in dry streaks that are a result of inadequate glue dispersion and thus, a weak overall binding.
Another methodology known in the art provides for the backbone of the book block to be facing upwardly while held between chains. A metal wheel is submerged in a bath of animal glue that is heated to approximately 150.degree. F. As it rotates, the metal wheel transfers adhesive to a black butyl rubber wheel. The adhesive on the black butyl rubber wheel is then transferred to the backbone of each book as the backbones pass under and in engagement with the rubber wheel. This methodology has several shortcomings. It is restricted to animal glues, the black butyl rubber wheel material destructs at temperatures above 160.degree. F., the wheel is stiff rubber that does not always conform to the shape of the backbone, and since animal glue is used, the bond provided by the glue is not as strong, flexible, durable or as compatible with other adhesives.
A third methodology is the extrusion of an adhesive which is usually hot melt glue by commercial equipment such as that provided by Nordson, Valco, Slautterback, or Spraymation. These systems allow for the use of hot melt adhesives but have several distinct disadvantages. For example, an extruded hot melt adhesive bond to the backbone is susceptible to delamination. Also, application inconsistencies can occur due to temperature and viscosity variances. Irregularity in beginning and ending of the application of the adhesive can cause the adhesive to run over the head and tail of the book. Stringing of adhesive on the trailing edge of the book can also occur when using this methodology.
It would be desirable to have an assembly available that could apply hot melt adhesive to the backbone of the book block without the disadvantages experienced by the existing methodologies.